1. Field of the Art
The present invention relates to a cement-based rust preventive composition for steel reinforcements for concrete (inclusive of steel frames). More particularly, the present invention relates to a cement-based rust preventive composition in which hydraulic setting is retarded.
2. Description of the Prior Art
From the viewpoint of reduction of the weight of concrete buildings and other structures and from the energy-saving viewpoint, interest in cellular concrete has been increasing, and so-called prefabrication has been promoted, whereby cellular concrete panels have come to be used in large quantities.
As a typical instance of cellular concrete, so-called ALC, viz. autoclaved light weight concrete, can be mentioned. This material is light concrete (LC) composed mainly of crystal calcium silicate hydrate of the tobermorite species, which is formed by hydrothermally curing a foamed and set product at a high temperature under a high pressure in an autoclave (A). It has a large commercial value as a stable construction material.
ALC now manufactured on an industrial scale is divided into a post-foam type and a pre-foam type according to the method for forming a cellular structure. In each case, when a hydraulic cement composition slurry is cast, a steel reinforcement having an appropriate shape is ordinarily arranged so as to reinforce a formed concrete product.
High-temperature, high-pressure, hydrothermal curing conditions to be applied to ALC cause extreme corrosion and rusting in steel reinforcements. Furthermore, as concrete per se is neutralized by carbon dioxide in the air and loses its alkalinity, rusting is similarly caused in steel reinforcements. Accordingly, it is necessary to subject steel reinforcements to a rust-resisting treatment.
As an example of the rust preventives used for giving resistance to rust to steel reinforcements, an agent comprising cement as a main component can be mentioned. The cement-based rust preventive comprises an aqueous dispersion of cement and auxiliary additives to be incorporated according to need. The rust-preventing treatment is ordinarily accomplished by dipping a steel reinforcement in a bath of the rust preventive comprising this aqueous dispersion to cover the surface of the steel reinforcement with a rust preventive component such as cement.
When this rust preventing treatment is practically carried out, a cement dispersion is prepared in a considerable amount necessary for dipping a structure formed by assembling steel reinforcements in this cement dispersion, and the so-prepared cement dispersion is stored in a rust preventive tank. Since cement can set hydraulically, utilization of a cement dispersion in the above described manner is very disadvantageous. More specifically, if the cement dispersion left after the rust preventing treatment is left standing, setting takes place so that the cement dispersion loses workability, resulting in great loss of the cement dispersion. Even if setting does not take place, the viscosity will be increased by a hydration reaction, and the amount of the cement adhering to the steel reinforcement cannot be controlled. This problem can be temporarily solved by the use of a setting retardant, but since the setting retarding effect of the known setting retardant does not last for a long time as far as I am aware, the problem remains still unsolved.
If a cement-based rust preventive which is controlled so that almost no hydration reaction occurs under ordinary rust preventing treatment conditions but the hydration reaction progresses under high-temperature high-pressure hydrothermal aging conditions could be developed, it would be a great contribution to the art.